It is expected that 16 of the 76 may not meet inclusion/exclusion criteria, leaving 60 consenting adults aged 18-65 years with DSM-IV bipolar disorder, which will be confirmed by the MINI (Sheehan et al.) Subjects must meet smoking inclusion criteria of smoking 10 or more cigarettes per day. Motivation to quit smoking (score of at least 7 on the Contemplation Ladder Scale) as well as stable mood status (Young Mania Rating Scale score of eight or less, Montgomery Asberg Depression Rating Scale Score of eight or less, with low scores on suicide aggression and psychotic items over a four-week period required. Subjects who have received pharmacological agents for smoking cessation such as bupropion, nicotine replacement treatment, or who have participated in behavioral treatment for smoking cessation more than three months before beginning the study will be permitted to enroll in the study. Anyone experiencing serious side-effects from varenicline in the past or who has already participated in a smoking cessation study with varenicline will be excluded.